The present invention relates to a tensioner for tensioning a belt or chain driving a camshaft of engine of motorcycle or automobile.
The tensioner is used to maintain a constant tension on a chain or belt when the belt or chain is slackened due to wear or elongation.
FIG. 5 shows a conventional tensioner disclosed by a Japanese Utility Model Application Laid-open No. 62-19015, which comprises a bored casing 1 to be installed perpendicularly on an equipment fastening bolts through two holes 1a provided on a wing portion thereof, a rotatable cylinder 2 rotatably inserted into the casing 1, a tension rod 3 engaged with a threaded portion of the rotatable cylinder 2 and urged by an urging force converted from a rotating force of the rotatable cylinder 2, a torsion spring 4 externally inserted over the rotatable cylinder 2 for driving the rotatable cylinder 2 and a non-circular bearing 5 fixed in the bored portion of the casing 1 for restraining the rotation of the tension rod 3. When the rotatable cylinder 2 is energized by the torsion spring 4 and the tension rod is abutted on a chain or belt, a rotational force of the torsion spring is transmitted to the tension rod. However, the rotational force is converted into a urging force on the rotatable cylinder 2 tensioning a chain or belt. In this manner, a constant tension is maintained on a chain or belt.
In this type of tensioner, it is necessary to close the casing hermetically in order to prevent a leakage of lubrificant filled in the casing 1. Therefore, a sealing bolt 7 is screwed in the lower end of the casing 1. A boot 6 is mounted between the upper end of the casing 1 and the neck portion of the tension rod so as to close the casing 1 hermetically, wherein the upper portion of the boot 6 is fixed on the tension rod with a snap ring 8 and the lower end is connected to the upper end of the casing 1 with a retainer 9. An orifice of "T" form air vent 11 is formed on a head piece 12 of the tension rod 3 so as to release the inner pressure variance of the casing due to an axial movement of the tension rod. The lower end of the air vent 11 is open over the oil level of lubrificant.
Also, it is necessary to lock an axial movement of the tension rod 3 during transport or storage. Therefore, a holder 10 is used to retain an urging force of the tension rod 3, of which hook portions 10a are inserted into the outer surface of the casing 1. The holder 10 is taken out when the tensioner is installed on an equipment.
However, the air vent 11 is always open during transport or storage. Accordingly, a leak of lubrificant from the air vent is unavoidable because of a slight vibration or positional variation during transport, or an expansion of the lubrificant when an environmental temperature increases during storage or transport.
The present invention was developed taking these situations in consideration and provides an air releasing and oil leak proof tensioner.